Thin film technology, wherein inorganic particles with sizes on the order of 1-100 nm are arranged in layers to form a film, is currently being used for an increasingly large number of different technological applications, including: information storage systems, chemical and biological sensors, fibre-optic systems, and magneto-optic and optical device.
A number of techniques are currently known for the preparation of such films. U.S. Pat. No. 6,805,904 discloses a method and structure that forms a multilayer nanoparticle thin film assembly by functionalizing a substrate with functional molecules and then replacing a stabilizer on a bottom surface of first nanoparticles with the functional molecules via surface ligand exchange to make a first nanoparticle. U.S. Pat. No. 6,676,729 relates to a method of making nanoparticles via metal salt reduction by firstly mixing metal salts in a solvent and then adding a reducing agent to the solvent. The nanoparticle dispersion is then stabilized and the nanoparticles precipitated from the nanoparticle dispersion. Finally, the nanoparticles are re-dispersed into the solvent. “Alternation of cationic and anionic polymeric materials and metal nanoparticles” (Decher et al., Science 1997, vol. 277: page 1232) describes alternation of cationic and anionic polymeric materials and metal nanoparticles. This is also described in “Layer-by-Layer Growth of Polymeric Nanoparticle Films Containing Monolayer Protected Gold Clusters” (Jocelyn F. Hicks, Young Seok-Shon, and Royce W. Murray, Langmuir, 2002, 18, 2288-2294) and “Rapid deposition of gold nanoparticle films with controlled thickness and structure by convective assembly” (B. G. Prevo, J. C. Fuller, III and O. D. Velev, Chem. Mater, in press (2004)). U.S. Pat. No. 6,162,532 describes a layer-by-layer formation of a film of compact arrays of magnetic nanoparticles for a magnetic storage medium.
However, all of the above described techniques comprise multiple steps to achieve formation of the nanoparticles on the substrate employed, including formation of the nanoparticles, selection of the size of nanoparticles and then deposition of the nanoparticles. At each step, loss or degradation of the end-product is risked and, in particular, when the nanoparticles are air-sensitive, resulting in restricting possible applications of the nanoparticles formed due to the resulting degradation of the nanoparticles formed caused by an ambient atmosphere. Some solutions have been proposed to obviate this disadvantage, for example, coating the particles with an amorphous and inert substance, such as silica or a polymer, or forming an oxide coating on the nanoparticles as described in U.S. Pat. No. 6,045,925. However, such coating results in a loss of some of magnetic properties of the nanoparticle film.